1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming a metal wiring of a semiconductor device capable of preventing metal by-products, which are generated in an area having high pattern density when over-etching time is inefficient due to a lack of a photosensitive film margin during a metal wiring etching process.
2. Description of the Prior Art
As semiconductor devices have been highly integrated, a critical dimension of a metal wiring is reduced so that it is difficult to define a pattern in a photo process. In addition, since the pattern is defined with reducing thickness of a photosensitive film, a margin of the photosensitive film is inefficient when performing an etching process so that it is difficult to determine an etching target. Accordingly, an over-etching time is inefficient, so metal by-products are generated. Thus, a bridge is formed between metal wirings, thereby reducing a yield rate of semiconductor devices.
FIGS. 1a to 1c are sectional views showing a conventional metal wiring forming method.
As shown in FIG. 1a, a lower metal wiring 2 is formed on a semiconductor substrate 1. Then, after forming an insulation layer 3 on an entire surface of the semiconductor substrate 1, the insulation layer 3 is selectively etched so as to form a contact hole 4 exposing a part of the lower metal wiring 2. Then, a tungsten layer (not shown) is deposited on the entire surface of the semiconductor substrate 1 including the contact hole 4 and a mechanical and chemical vapor deposition process is carried out in order to form a conductive plug 9 for filling the contact hole 4.
After that, a metal layer 9 for forming an upper metal wiring and including a first Ti/TiN layer 6, an Al layer 7, and a second Ti/TiN layer 8, which are sequentially deposited, is formed on the entire surface of the semiconductor substrate 1 including the conductive plug 5. At this time, the first and second Ti layers act as an adhesive layer, and the first TiN layer acts as a diffusion barrier. In addition, the Al layer acts as a conductive layer for transferring an electric signal, and the second TiN layer acts as an anti-reflective coating layer for reducing light reflection when patterning the photosensitive film.
Then, as shown in FIG. 1b, after coating the photosensitive film on the metal layer 9, an exposure and development process is carried out so as to form a photosensitive film pattern 20 for exposing an upper metal wiring region (not shown). At this time, the photosensitive film acts as an etching mask when a next etching process is carried out, so it is required for the photosensitive film to have sufficient thickness. As an integration degree of the metal wirings increases, a line width and an interval between metal wirings are reduced and a height of the metal wiring is increased. Thus, the thickness of the photosensitive film coated on the metal layer must be increased in proportional to the height of the metal wiring.
After that, the metal layer is dry-etched by using the photosensitive film pattern 20 as a mask. In addition, as shown in FIG. 1c, an upper metal wiring 10 connected to the lower metal wiring 2 through the conductive plug 5 is formed. When the dry-etching process is carried out, plasma including activated Cl2, BCl3, and N2 gases is used as etching gas. Then, the photosensitive film pattern is removed.
FIG. 2 is a sectional view for explaining problems of a conventional semiconductor manufacturing process.
As an integration degree of the semiconductor device increases, a line width and an interval between metal wirings are reduced and a height of the metal wiring is increased. When fabricating the metal wiring having the high integration degree by using the conventional semiconductor manufacturing process, problems occur as follows:
Firstly, when Al is used as a metal layer for the metal wiring, the metal layer cannot be constantly maintained in a predetermined shape because Al has superior ductility. For this reason, 5% of Cu is mixed with Al when forming the metal layer. However, Cu is not uniformly distributed into the metal layer, but concentrated at an interfacial surface between the metal layer and the first Ti/TiN layer in the form of an Al2Cu layer.
Thus, when the upper metal wiring is formed by dry-etching the metal layer, the Al2Cu layer aligned between the first Ti/TiN layer and an Al layer acts as a barrier because the Al2Cu layer has relatively lower vapor pressure as compared with the Al layer. Accordingly, an activated Cl radical is not easily etched so that metal by-products having a rice shape are created on a surface of the insulation layer (refer to “A” in FIG. 2).
Due to the metal by-products, an etch stop layer is detected before the Al2Cu layer is etched so that an over-etching is insufficient carried out. Thus, the metal by-products cannot be completely removed, thereby causing a bridge between metal wiring.
In order to solve the above problem, a physical etching process has been suggested instead of a chemical etching process. However, the physical etching process requires increased bias power, so selectivity of the photosensitive film is lowered, thereby forming an attack or a slope in the metal wiring.